Electrical condenser



C. L. RECHARDS ELECTRICAL CONDENSER Filed. Nov. 16, 1944 FIG. 5

ENVENTOR CLAUDE mucosa RICHARDS 1 i/(m ATTORNEY.

Patented Feb. 1, 1949 ELECTRICAL CONDENSER Claude Langdon Richards, London, England, as-

signor to The Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application November 16, 1944, Serial No. 563,723 In Great Britain June 25, 1943 Section 1, Public Law 690, August a, 1946 Patent expires June 25, 1963 4 Claims.

This invention relates to electrical condensers having a solid dielectric and has for its object to provide a simple solid dielectric condenser affording the possibility of varying the capacity in a very simple manner.

According to the present invention conducting particles and particles of the insulating material which is to constitute the dielectric are mixed together, a binder is added if necessary and the mixture is moulded or otherwise formed into the desired shape and subjected to the requisite treatment, such as heating, air-drying or the like, or sintering, in accordance with the nature of the materials in the mix, to produce a composite solid body to which the condenser connections are applied. The particle sizes of the insulating and conducting particles and their relative quantities are so chosen that the individual conducting particles are substantially all insulated from adjacent conducting particles by interposed insulating particles; suitably the particle sizes of the different components are of the same order of magnitude. Advantageously, the dielectric is a ceramic in which case the conducting particles are incorporated in the ceramic mix which is then subjected to the usual treatment for the production of a ceramic body. In general, the ceramic willact as a binder for the conductive particles, so that a solid body is obtained without the use of a separate binder.

The conductive particles may be carbon or a metal which is not affected by the process involved in the manufacture of the composite bodies. Examples of suitable dielectric materials are mica and titanium dioxide. Preferably the linear dimensions of the conductive particles are of the order of 40 microns. The quantities of conductive and insulating particles with particles of relatively uniform size are advantageously so chosen that W1 being the weight of the conductive material in the mix.

We the weight of the insulator, together with the binder, if any.

D1 the specific gravity of the conductive material.

D2 the specific gravity of the mixture of insulation plus binder.

For uniform materials of relatively the same density this condition is equivalent to "the volume of dielectric material being twice that of conductive material.

If the composite body is in the form of a rod with one contact secured to one end and having a sliding contact arranged to slide along the length of the red the efiect would be that of a large number of condensers formed by the metal particles separated by the ceramic or other insulating particles. These individual minute condensers can be regarded as joined in series along the length of the rod and, therefore, the greater length of rod between the fixed and moving contacts, the smaller would be the capacity of the condenser. The rod need not, of course, be straight but could be moulded into a circular shape so that the sliding contact could be arranged so as to have a rotary motion similar to the well-known rotary resistances or potentiometers.

In general the shape of the capacitative material of the condenser should be so chosen that at any transverse section, i. e. a section in a plane at right angles to the path of the capacitative current, the ratio (Periphery) Cross sectional area is greater than and preferably greater than 100, the periphery and area being measured in the same units. For a rectangular cross-section this is equivalent to the width being not less than 11 times the thickness, and preferably not less than 23 times the thickness. Moreover, when the periphery is polygonal the condenser connections or contacts should be arranged to make contact with the longest side of the polygon.

An alternative would be to mould the mixture into the form of a rectangular plate or rod and arrange one fixed contact to cover the entire area of one side of the plate or rod. This can be done, for example, by means of the wellknown method of silvering used with ceramics.

A sliding contact in the form of a plate could then be arranged to make contact with more or less of the area of the opposite side of the plate .or rod. The effect in this case would be that of a number of minute condensers joined in series between the fixed plate and the movwhich the composite body is of substantially annular form Fig. 2 is a perspective viewyof a construction in which the composite body is in the'form of a straight strip-like rod I Fig. 3 is a side vie-w of a construction in which one fixed contact covers the entire area of one side of a plate Fig. 4 is a side view, in part in section, of a trimmer condenser according to the invention.

Fig. 5 is a view in part in section along the line V-V in Fig. 4. i

In Fig. 1 the capacitative member is in the form of a rod I of progressively increasing crosssection and curved so that its centre line lies substantially in a circle. One end of the rod I is provided with a fixed contact member 2, the other contact being established by a contact member 3 slidable on 'the surface of the red I. The sliding contact member 3 is carried by a spring arm 4 which is secured to a shaft 5 concentric with, and extending at right angles to the plane of, the circle described by the centre line of the rod I. Thus, by rotating the shaft '5 the capacity can be adjusted;' the law according to which the capacity varies with the angular setting is determined by the divergence of the rod I in the longitudinal direction.

-In Fig. 2 the-capacitative material is in the form of a straight strip 6 having a fixed contact member 2 at one'end. The 'secondcontac't is afforded by a pair of contact members I on opposite sides of the strip 6. These contact members areelectrically and mechanically united by a bridge '8, so that they are adjusted simultaneously and identically.

In Fig. 3 the plate 9 of capacitative material is provided with a fixed contact 2 covering the whole of one side; cooperating with the opposite side of the plate 9v is the second contact in the form of a plate I0 which is slidable in relation to the plate 9' and'can be caused to cover all or part denser.

I3 is enclosed between the contact plates II, thereby altering the capacity of the condenser. A shaped .spring made from fiat material such as spring brass I 9 is arranged to exert spring pressure on the screw I4 so that the disc I2 is constrained to rotate on the raised .part 20 of the moulding I6. The slotted head of the screw I4 is accessible for adjustment through the aperture ZI. The-contact plates II/ are kept in close contact with thecapacitative'disc I2 by means of the formed springs 22, which at the same time restrict sideways movement of the plates I I by the lips 23 on the springs 22 interacting with recesses 24 in the body I5. Extensions 25 of these springs 22 are used as. contact terminals for the com I claim:

1. An electrical condenser comprising a discshaped composite body having a segmental aperture therein and comprising particles of insulating dielectric material and electrically conductive particles insulated from each other by interposed particles of said insulating dielectric material, a plurality of condenser ,electrodes in capacitative relationship with said body, said electrodes consisting of two semicircular metallic plates in contact with opposite surface portions of said body, and means to rotate said body relative to said plates to thereby vary the extent to which the non-apertured portion of the disc is interposed between said electrodes.

2. An electric condenser comprising a discshaped composite body having a segmental aperture therein andcomprising ceramic particles and metallic particles electrically insulated from each other by said ceramic particles, two condenser electrodes in capacitative relationship with said body, said electrodes consisting of two semi-circular metallic plates in' contact with opposite surface portions of said body, and means to rotate said body relative to said plates to thereby vary the extent to which the no the disc isinterposedbetween said electrodes.

3. An electrical. condenser, comprising a discshaped composite body having asegmental aperture therein and comprising ceramic particles and carbon particles insulated from each other by said ceramic, particles, a plurality of condenser electrodes in capacitative relationship with said body, said electrodes consisting of two semi-circular metallic plates in contact-with opposite surface portions ofzsaid body, and means to rotate said body relative .to said plates to thereby vary the asdesired ofv the surface, with corresponding variations in the capacity.

Figs. 4 and 5 show a trimmer condenser constructed in accordance with the invention. The mechanical construction illustrated in Figs. 4 and 5 takes the form of two semi-circular plates II forming the contact [plates of the condenser.'

Between the plates I I is the capacitative material in the form of a disc I2, with a semi-circular aperture I3. The periphery of the disc I2 is proextent to which the non-apertured portion of the disc is interposed, between the electrodes.

4. An electrical condenser comprising a discshaped composite body having a segmental aperture therein and comprising ceramic particles and particles of conducting material electrically insulated from each other by said ceramic particles, the relative proportions of the ceramic particles and, the conducting particles being determined in accordance with the following equation:

vided with gear teeth meshing with the screw thread I4.

The two contact plates II, together with the capacitative disc I2 and the operative screw I4 are housed in a moulded container, constructed in two halves I5 and I6, joined together by means of the screws I1, and provided with fixing holes I8.

Rotation of the screw I4 rotates the capacitae tive disc [2, so that more or less of the air space -aperture.d portion of r face portions of said body, a.nd means to rotate said body relative to said plates to thereby vary the extent to which the non-apertured portions of the disc is interposed between the electrodes.

. CLAUDE LANGDON RICHARDS.

Parvillee Apr. 12, 1898 Papinl -1 Mar. 30, 1920 Number White Oct. 18, 1921 15 Number Number Name Date Shrader Sept. 2, 1924 Hill Apr. 21, 1925 Kirby June 15, 1926 Murray Sept. 6, 1927 Dublller June 10, 1930 Ruben Nov. 11, 1930 Benkelman May 16, 1933 Lips Dec. 15, 1942 FOREIGN PATENTS Country Date Germany May 30, 1901 Germany Nov. 8, 1933 

